The power and speed of consumer and business desktop computers has recently reached the level that computers of even average performance frequently include multi-media capability. For most of these computers a microphone is an indispensable component. Microphones are used with computers not only for simple digital recording of sounds, but also for telephony, speech recognition applications, and the like.
Many computers employ a free standing microphone plugged in to the computer at a convenient (or sometimes inconvenient) location. Many manufacturers and users prefer, however, to integrate as many of the computer's peripheral components as possible to make setup easier and to reduce clutter on or around the desktop. Accordingly, some manufacturers are incorporating microphones into the video monitor, often with a port on the face (i.e., bezel) of the monitor pointing toward the user. Some of these microphones are directional, utilizing two ports. While incorporation of the microphone into the monitor bezel addresses the integration concerns noted above, it causes some additional problems.
In particular, the electronic components of video monitors emit electromagnetic radiation that frequently can be picked up by a microphone mounted in the monitor bezel--this electromagnetic radiation is detected as noise or interference, often sounding, e.g., like a hum or buzz. Electromagnetic radiation detected as noise or interference will be referred to hereafter as electromagnetic interference (or "EMI")
Many commercially available microphone cartridges are provided with some shielding from EMI. Nevertheless, leakage of EMI is common. Typically, shielding is partially accomplished by mounting the microphone element in a cylindrical metal enclosure or "can" which holds the microphone element. Usually the can holds a small circuit board at its back end, the electrical leads being secured to this circuit board. The can provides shielding from the sides, but does not shield the front or back of the microphone. Some shielding from the back may be provided by, e.g., a metal foil layer in the circuit board. Directional microphones, however, necessarily include a rear sound port through the circuit board, which obviously cannot be covered with shielding. Quality control in assembling the cartridges may sometimes be less than optimal, giving rise to leakage. Taking all of these practical considerations into account, applicant has found that conventional shielded microphone cartridges, even those of reasonably good quality, when employed in the bezel of a video monitor, detect a significant level of undesirable EMI.
Some electronic devices incorporate housings with electronic shielding to prevent (or at least reduce) significant emissions of EMI, so that the electronic device will not cause critical interference with other types of electronic devices designed to detect and receive electromagnetic radiation--the FCC has issued a variety of regulations governing such emissions and required shielding for some devices. Such shielding in these housings typically is not constructed in a manner that provides shielding of internal components from one another, however.